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Part 8: player controls: left+right and jump+fall mechanics
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Walking on platforms, falling down off the ledge, jumping, staying
within play-field, detecting when falling from too high (will just
disable controls for 1s in this version).

No ladder mechanics yet (will be part 9)
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@ped7g
ped7g committed Feb 9, 2020
1 parent fe8b226 commit 35d9188
Showing 1 changed file with 179 additions and 70 deletions.
249 changes: 179 additions & 70 deletions SpecBong.asm
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Original file line number Diff line number Diff line change
Expand Up @@ -164,6 +164,11 @@ InitBallsLoop:
ld (ix+S_SPRITE_4B_ATTR.y),206 ; near bottom of paper area
ld (ix+S_SPRITE_4B_ATTR.mrx8),0 ; clear pal offset, mirrors, rotate, x8
ld (ix+S_SPRITE_4B_ATTR.vpat),$80 + 2 ; pattern "2" (player
;DEBUG position for testing the jump+fall mechanics
ld (ix+S_SPRITE_4B_ATTR.x),32+100
ld (ix+S_SPRITE_4B_ATTR.y),32
ld a,255
ld (Player1SafeLandingY),a

; main loop of the game
GameLoop:
Expand Down Expand Up @@ -379,90 +384,177 @@ GetPlatformPosUnder:
;-------------------------------------------------------------------------------------
; "AI" subroutines

;-------------------------------------------------------------------------------------
; Part 8 - player controls: left+right and jump+fall mechanics

Player1MoveByControls:
; update "cooldown" of fire button to allow it only once per 10 frames
ld a,(Player1FireCoolDown)
; update "cooldown" of controls if there's some delay needed
ld a,(Player1ControlsCoolDown)
sub 1 ; SUB to update also carry flag
adc a,0 ; clamp the value to 0 to not go -1
ld (Player1FireCoolDown),a
; just DEBUG: up/down/left/right over whole screen, fire changing animation frame
ld (Player1ControlsCoolDown),a
ret nz ; don't do anything with player during "cooldown"
ld ix,SprPlayer
; calculate nearest platform at x-3 and x+3
ld l,(ix+S_SPRITE_4B_ATTR.x)
ld a,l
sub 3 ; not caring about edge cases, only works for expected X values
ld (ix+S_SPRITE_4B_ATTR.x),a ; posX-3
call GetPlatformPosUnder
sub 16 ; player wants platform at +16 from player.Y
ld h,a
ld a,l
add a,3
ld (ix+S_SPRITE_4B_ATTR.x),a
call GetPlatformPosUnder
sub 16 ; player wants platform at +16 from player.Y
ld (ix+S_SPRITE_4B_ATTR.x),l ; restore posX
cp h
jr nc,.keepHigherPlatform
ld h,a
.keepHigherPlatform:
; H = -16 + min(PlatformY[-3], PlatformY[+3]), C = extras of right platform, L = posX
ld a,(Player1JumpIdx)
or a
jr z,.notInTableJump
.doTheTableJumpFall:
; table jump/fall .. keep doing it until landing (no controls accepted)
ld e,a
ld d,high PlayerJumpYOfs ; address of current DeltaY
cp 255
adc a,0 ; increment it until it will reach 255, then keep 255
ld (Player1JumpIdx),a
; adjust posX by jump direction (3 of 4 frames)
ld a,(TotalFrames)
and 3
jr z,.skipJumpPosXupdate
ld a,(Player1JumpDir)
call .updateXPosAplusL
.skipJumpPosXupdate:
; adjust posY by jump/fall table
ld a,(de) ; deltaY for current jumpIdx
add a,(ix+S_SPRITE_4B_ATTR.y)
cp h ; compare with platform Y
jr z,.didLand
jr nc,.didLand
; still falling
ld (ix+S_SPRITE_4B_ATTR.y),a
ret
.didLand:
ld (ix+S_SPRITE_4B_ATTR.y),h ; land *at* platform precisely
xor a
ld (Player1JumpIdx),a ; next frame do regular AI (no more jump table)
ld (ix+S_SPRITE_4B_ATTR.vpat),$80+4 ; landing sprite
ld a,4 ; keep landing sprite for 4 frames
ld (Player1ControlsCoolDown),a
; check if landing was too hard
ld a,(Player1SafeLandingY)
cp h
ret nc
; lands too hard, "die" - just disable controls for 1s for now
ld a,50
ld (Player1ControlsCoolDown),a
ret

.notInTableJump:
; H = -16 + min(PlatformY[-3], PlatformY[+3]), C = extras of right platform, L = posX
; if landing pattern, turn it into normal pattern
ld a,(ix+S_SPRITE_4B_ATTR.vpat)
cp $80+4
jr nz,.notLandingSprite
ld (ix+S_SPRITE_4B_ATTR.vpat),$80 ; reset sprite to 0
.notLandingSprite:
;TODO if ladder pattern, do the ladder AI
; if regular pattern, do regular movement handling
; check if stands at platform +-1px (and align with platform)
ld a,(ix+S_SPRITE_4B_ATTR.y)
sub h
adc a,0 ; turn -1/0/+1 into 0/+1
cp 2
jr c,.almostAtPlatform
; too much above platform, turn it into freefall (table jump)
xor a
ld (Player1JumpDir),a
ld a,low PlayerFallYOfs
jr .doTheTableJumpFall ; and do the first tick of fall this frame already

.almostAtPlatform:
ld (ix+S_SPRITE_4B_ATTR.y),h ; place him precisely at platform
; refresh safe landing Y
ld a,18
add a,h
ld (Player1SafeLandingY),a
ld a,(Player1Controls)
ld b,a ; keep control bits around in B for simplicity
; HL = current X coordinate (9 bit)
ld l,(ix+S_SPRITE_4B_ATTR.x)
ld h,(ix+S_SPRITE_4B_ATTR.mrx8)
ld c,h ; preserve current mirrorX
bit JOY_BIT_FIRE,b
jr z,.notJumpPressed
; start a new jump sequence
ld a,$80+3 ; jump pattern + visible
ld (ix+S_SPRITE_4B_ATTR.vpat),a
xor a
bit JOY_BIT_LEFT,b
jr z,.noLeftJump
dec a
.noLeftJump:
bit JOY_BIT_RIGHT,b
jr z,.notGoingRight
inc hl
inc hl ; X += 2
res 3,c ; mirrorX=0 (face right)
.notGoingRight:
jr z,.noRightJump
inc a
.noRightJump:
ld (Player1JumpDir),a
ld a,low PlayerJumpYOfs
jp .doTheTableJumpFall ; and do the first tick of jump this frame already

.notJumpPressed:
/* TODO
if up/down is pressed {
near ladder +-Npx -> switch to ladder pattern, adjust Y -> end
else reset dir controls + continue (stands)
}
*/
; C = extras of right platform, L = posX, B = user controls
bit JOY_BIT_LEFT,b
jr z,.notGoingLeft
dec hl
dec hl ; X -= 2
set 3,c ; mirrorX=1 (face left)
; move left
set 3,(ix+S_SPRITE_4B_ATTR.mrx8) ; set MirroX flag (to face left)
ld a,(TotalFrames)
and 3
jr z,.animateRunPattern ; one frame out of 4 don't move but animate (0.75px speed)
ld a,-1
jr .updateXPosAplusL

.notGoingLeft:
; sanitize HL to values range 32..272 (16px sprite fully visible in PAPER area)
ld de,32
; first clear top bits of H to keep only "x8" bit of it (remove mirrors/rot/pal data)
rr h ; Fcarry = x8
ld h,0
rl h ; x8 back to H, Fcarry=0 (for sbc)
sbc hl,de
add hl,de ; Fc=1 when HL is 0..31
jr nc,.XposIs32plus
ex de,hl ; for 0..31 reset the Xpos=HL=32
.XposIs32plus: ; (there was "272" constant in previous part => bug, now fixed)
ld de,32+256-16+1 ; 273 - first position when sprite has one px in border
or a ; Fc=0
sbc hl,de
add hl,de ; Fc=1 when HL is 32..272
jr c,.XposIsValid
ex de,hl
dec hl ; for 273+ reset the Xpos=HL=272
.XposIsValid:
; store the sanitized X post and new mirrorX to player sprite values
ld a,c
and ~1 ; clear x8 bit (preserves only mirror/rotate/...)
or h ; merge x8 back
ld (ix+S_SPRITE_4B_ATTR.x),l
ld (ix+S_SPRITE_4B_ATTR.mrx8),a
; vertical movement
ld a,(ix+S_SPRITE_4B_ATTR.y)
bit JOY_BIT_UP,b
jr z,.notGoingUp
dec a
dec a ; Y -= 2
cp 32 ; sanitize right here
jr nc,.notGoingUp
ld a,32 ; 0..31 -> Y=32
.notGoingUp:
bit JOY_BIT_DOWN,b
jr z,.notGoingDown
inc a
inc a ; Y += 2
cp 32+192-16+1 ; sanitize right here (209+ is outside of PAPER area)
jr c,.notGoingDown
ld a,32+192-16 ; 209..255 -> Y=208 (was 207 in previous part = bug)
.notGoingDown:
ld (ix+S_SPRITE_4B_ATTR.y),a
; change through all 64 sprite patterns when pressing fire
bit JOY_BIT_FIRE,b
ret z ; Player1 movement done - no fire button
ld a,(Player1FireCoolDown)
or a
ret nz ; check "cooldown" of fire, ignore button if still cooling down
ld a,10
ld (Player1FireCoolDown),a ; set new "cooldown" if pattern will change
bit JOY_BIT_RIGHT,b
jr z,.notGoingRight
; move right
res 3,(ix+S_SPRITE_4B_ATTR.mrx8) ; reset MirroX flag (to face right)
ld a,(TotalFrames)
and 3
jr z,.animateRunPattern ; one frame out of 4 don't move but animate (0.75px speed)
ld a,+1
jr .updateXPosAplusL

.animateRunPattern:
; animate pattern 0..3 frames (in case he holds left or right) (if not, it will be zeroed)
ld a,(ix+S_SPRITE_4B_ATTR.vpat)
inc a
and ~64 ; force the pattern to stay 0..63 and keep +128 for "visible"
and %1'0'000011 ; force pattern to stay 0..3 (+visible flag)
ld (ix+S_SPRITE_4B_ATTR.vpat),a
ret

.notGoingRight:
; not going anywhere
ld (ix+S_SPRITE_4B_ATTR.vpat),$80 ; reset to frame 0
ret

.updateXPosAplusL:
add a,l ; add A and L to get final posX
cp 32
ret c ; way too left, don't update
cp 32+192-16+1
ret nc ; way too right, don't update
ld (ix+S_SPRITE_4B_ATTR.x),a ; valid X: 32..32+192-16
ret

SnowballsAI:
ld ix,SprSnowballs
ld de,S_SPRITE_4B_ATTR
Expand Down Expand Up @@ -613,8 +705,14 @@ CollisionFxCount: ; count the dynamically created extra FX sprites dis
; bits encoding inputs as Kempston/MD: https://wiki.specnext.dev/Kempston_Joystick
Player1Controls:
DB 0
Player1FireCoolDown:
Player1ControlsCoolDown:
DB 0
Player1JumpIdx: ; when non-zero, player is jumping (and it is index to PlayerJumpYOfs table)
DB 0
Player1JumpDir:
DB 0 ; -1/0/+1 depending if the jump has direction or not
Player1SafeLandingY:
DB 0 ; last known safe landing Y (will be +18 to current Y when *at* platform)

; reserve full 128 sprites 4B type (this demo will not use 5B type sprites)
ALIGN 256 ; aligned at 256B boundary w/o particular reason (yet)
Expand Down Expand Up @@ -671,6 +769,17 @@ PlatformsCollisionData: ; the Y-coord of platforms are in sprite coordinates
DB 97, 1, 156, 1, 214, 1, 255, 0, 255, 0, 255, 0, 255, 0, 255, 0
PlatformsCollisionDataEnd:

; this is 32B table which should precisely fit at the end of 256B page
; i.e. at $xxE0..$xxFF addresses - it will be used by the code to stay at last item
PlayerJumpYOfs:
DB -2, -2, -2, -1, -1, -1, -1, -1
DB -1, -1, -1, 0, -1, 0, -1, 0
DB 0, 0, 0, 1, 0, 1, 0, 1
DB 1, 1, 1, 1
PlayerFallYOfs: ; first item of free-fall w/o jump
DB 1, 1, 1, 2 ; last item to be used repeatedly
ASSERT low $ == 0 ; did reach end of aligned 256B block?

;-------------------------------------------------------------------------------------
; reserve area for stack at $B800..$BFFF region
ORG $B800
Expand Down

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